Arcellx announces new data from expansion study of CART-ddBCMA

Arcellx announced new clinical data from its Phase 1 expansion study of CART-ddBCMA, now known as anitocabtagene autoleucel, or anito-cel. Anito-cel utilizes a novel D-Domain BCMA binder that is compact and stable, which results in a drug product with a high proportion of CAR+ cells and high surface expression, potentially enhancing antigen binding and more efficient Multiple Myeloma cell killing. The data continue to demonstrate robust long-term responses with median duration of response, progression free survival, or PFS, and overall survival rate not reached. The data are from an October 15 data cut, with median follow-up after anito-cel infusion of 26.5 months. These latest study findings will be presented as an oral presentation during the 65th American Society of Hematology, or ASH. As of October 15, 38 patients were evaluable for efficacy and safety analysis based on a median follow-up of 26.5 months following treatment. These evaluable patients comprised the dose escalation cohorts for the first dose level and the second dose level and a dose expansion cohort at 100 million CAR+ T cells. The median dose administered to patients in the first dose level and dose expansion cohorts was 115M CAR+ T cells. All patients evaluable for this analysis have poor prognostic factors with 38 of 38 patients triple-refractory, 26 of 38 penta-refractory, and 34 of 38 refractory to last line of treatment under International Myeloma Working Group, or IMWG, criteria. Additionally, 9 of 38 patients had high tumor burden with greater than 60% bone marrow plasma, or BMPC, cells, 13 of 38 patients had extra-medullary disease and 11 of 38 patients had high-risk cytogenetics at screening/baseline. Further, 24 of 38 had at least one high-risk clinical feature, defined as presence of EMD, BMPC greater than60%, or Beta 2 microglobulin greater than 5.5 mg/L at screening/baseline. All 38 patients had at least three prior lines of therapy. The interim anito-cel Phase 1 clinical results demonstrate deep and durable responses in patients with poor prognostic factors. Of the 38 evaluable patients with a median follow-up of 26.5 months: 100% overall response rate, or ORR. achieved in all patients per IMWG criteria; 29 of 38 evaluable patients achieved a complete response, or CR, or a stringent complete response; 35 of 38 patients achieved a very good partial response or higher. Of those evaluable for MRD testing to date, 25 were MRD-negative at a minimum of 10-5 sensitivity. Median duration of response, progression free survival and overall survival were not reached at the time of the October 15 data cut. While median PFS is yet to be reached, the estimated Kaplan-Meier median progression free survival for the study population was 28 months at the time of the data cut with 26.5 months of median follow-up. The Kaplan-Meier method estimated PFS rates for 6, 12, 18 and 24 months were 92%, 76%, 64% and 56%, respectively. Durable responses were also observed in patients with high-risk features and high-risk cytogenetics. Anito-cel dosed at RP2D continues to be well-tolerated at the time of the October 15, 2023 data cut: Adverse events with anito-cel, including CRS and ICANS, were manageable. No cases of grade 3 CRS and only one case of grade 3 ICANS event with no additional cases from previously reported. No tissue-targeted toxicities were observed No cases of delayed neurotoxicity events or parkinsonian symptoms were observed.